Positive-working photosensitive elements containing crosslinked beads and process of use

ABSTRACT

Photosensitive coating composition consisting essentially of an ethylenic unsaturated compound, a photoinitiator or photoinitiator system, an organic polymeric binder, discrete, substantially nonswellable, nonagglomerating, crosslinked beads, 0.1 to 4.0 μm in average diameter size, at least 90% of the beads by population below 6.0 μm, as defined and a solvent for the binder. The crosslinked beads can be present in positive-working systems. Preferred beads are trimethylolpropane triacrylate. The coating composition can be dried quickly into the form of a film which is useful as a dry film photoresist.

This is a divisional of application Ser. No. 756,698, filed July 19,1985, now U.S. Pat. No. 4,601,970, which is a divisional of applicationSer. No. 611,870, filed May 18, 1984, now U.S. Pat. No. 4,551,415, whichis a continuation-in-part of application Ser. No. 370,991, filed Apr.22, 1982, now abandoned.

TECHNICAL FIELD

This invention relates to photosensitive coating compositions. Moreparticularly this invention relates to photosensitive compositions inwhich a portion of the binder component is replaced by crosslinkedpolymeric beads. This invention further relates to dry photosensitivefilm, containing crosslinked polymeric beads.

BACKGROUND ART

Photopolymerizable compositions prepared from ethylenically unsaturatedmonomeric compounds, photoinitiators, organic polymeric binders as wellas other additives are known to be useful for the preparation of dryfilm resists and for other uses. The components that are used in thepreparation of the photopolymerizable compositions are generally mixedin a suitable solvent or solvents for the polymeric binder, and thecomposition is formed into a dry film by coating and removing thesolvent, e.g., by extrusion coating, or other means to form dry filmsknown to those skilled in the art.

Photopolymerizable compositions, particularly in dry layer form, arebecoming increasingly popular for printing plates and photoresist films.Dry film photoresists, for example, have many advantages over liquidphotoresists in the manufacture of printing circuits. In fact, dry filmphotoresists are becoming so popular that manufacturing capability ofthe plant may quickly be reached. One problem that occurs in themanufacture of photoresist films is the ability of such films to bedried quickly and efficiently. Drying of photopolymerizable coatings ina hot air dryer is influenced by many variables, e.g., thickness andsolids concentration of the coatings, characteristics of the solvents,solvent interaction with the composition to be coated, temperature ofthe film, temperature of the air, air velocity, direction andturbulence, relative humidity, etc. Generally, drying may be consideredto take place in two stages. In the first stage, the rate of drying isabout the same as the rate for removal of pure solvent, the limitingfactor is the rate at which solvent molecules can be removed from thesurface (or from the air space above the surface) of the coating. Thesupply of heat energy to the coating and the air velocity aresignificant factors in this first drying stage. In the second stage, asthe coating becomes more concentrated, drying slows down and is limitedby the rate of diffusion of solvent molecules from the interior of thecoating to the air surface of the coating. In this second drying stagenot only are the temperature and air velocity important but someinternal factors, e.g., the interaction between the solvent and solute,etc., are important as well.

In view of the many problems associated with the drying ofphotopolymerizable coatings, it is known that the temperature used todry such coatings, should be less than the temperature at which bubblesform in the coating. The formation of bubbles is undesirable becauseonce formed the bubbles may not collapse or if they do break the coatingmay be too viscous and uneven spots are formed in the layer. As a resultdryers are usually arranged in zones, the temperature in each zone beingheld at some safe margin below the temperature that will cause bubblesto appear in the coating.

An additional limitation on the drying rate is the tendency of polymersolutions to "skin over". Too-rapid drying, especially in initialstages, results in formation of a substantially dry skin on the surfaceof the coating, but solvent-rich coating is stil present below the skinwhich once dried does not readily redissolve in the underlying solvent.The skin thus acts as a barrier to solvent evaporation. This problem maybe alleviated by slower drying, e.g., lower temperature, air velocity,adding a higher boiling solvent, etc. Slower drying, however, results ina slower production of photopolymerizable films and elements.

It has been found surprisingly that by replacing a portion of thedissolved polymeric binder of a photopolymerizable coating compositionwith crosslinked polymeric beads which are insoluble in the coatingsolvent dry photopolymerizable films and elements can be prepared moreefficiently. The photopolymerizable layers of such films and elementsdry more quickly with less risk of bubble formation. Production canthereby be increased even though there is no increase in actual size ofthe manufacturing facility. The photopolymerizable layer has been foundto retain desirable properties in spite of the presence of thecrosslinked polymeric beads since they can be designed to closely matchthe refractive index of the soluble polymeric binder thereby minimizinglight scattering often associated with inorganic insoluble fillers. Forexample, the photographic speed, adhesion to copper, clarity orresolution, and flexibility of the photopolymerizable layer aremaintained.

DISCLOSURE OF THE INVENTION

In accordance with this invention there is provided a photosensitivecoating composition consisting essentially of

(a) 5 to 45% by weight based on the weight of components (a) to (d) ofat least one nongaseous, ethylenically unsaturated compound having atleast one terminal ethylenic group, said compound being capable offorming a high polymer by free-radical initiated, chain-propagatingaddition polymerization;

(b) 0.05 to 10% by weight based on the weight of components (a) and (d)of an organic, radiation-sensitive, free-radical generating system,activatable by actinic radiation which initiates polymerization of theunsaturated compound;

(c) at least one organic polymeric binder;

(d) discrete, substantially nonswellable crosslinked polymeric beadshaving an average diameter in the range of 0.02 to 4.0 μm, wherein atleast 90% of the beads by population are below 6 μm, the beads beinginsoluble and nonagglomerating in a solvent for the organic polymericbinder component, said crosslinked polymeric beads are taken from theclass consisting of homopolymers and copolymers of monomers containingtwo or more free-radical polymerizable double bonds per molecule, andcopolymers of at least one of said monomers and at least one monomerhaving one terminal ethylenic group, the total weight percent of thecombination of components (c) and (d) based on the total weight ofcomponents (a) to (d) being 40 to 70% by weight, component (d) beingpresent in an amount of 15 to 90% by weight based on the weight ofcomponents (c) and (d); and

(e) at least one solvent for components (a), (b) and (c), thecrosslinked polymeric beads being resistant to absorbing or beingplasticized by any component or mixture of components of the coatingcomposition, being mutually compatible with the dissolved ingredients a,b, c and e of the coating composition in which said beads are dispersed,and remaining dispersed therein as said coating is dried.

In accordance with another embodiment of this invention there isprovided a positive-working photosensitive element comprising a supportbearing a releasably bonded dry layer of a positive-working compositionconsisting essentially of the reaction product of (a) at least onephotosolubilizable material and (c) at least one organic polymericbinder, components (a) and (c) being present in amounts of 50 to 95% and5 to 50% by weight, respectively, based on the total weight ofcomponents (a) and (c); (b) a radiation-sensitive compound or systemactivatable by actinic radiation, 0 to 10% by weight based on the totalweight of the composition; and (d) discrete, substantially nonswellablecrosslinked polymeric beads having an average diameter in the range of0.02 to 4.0 μm, wherein at least 90% of the beads by population arebelow 6 μm, the beads being insoluble and nonagglomerating in a solventfor the organic polymeric binder component, and remaining dispersed insaid layer, the weight of component (d) being 20 to 65% by weight basedon the total weight of the composition.

The photopolymerizable coating compositions of the invention consistessentially of at least one nongaseous ethylenically unsaturatedcompound containing at least one terminal ethylenic group (a), anorganic, radiation-sensitive free-radical generating photoinitiator orphotoinitiator system (b), at least one organic polymeric binder (c),discrete, substantially nonswellable crosslinked polymeric beads (d)which replace a portion of the polymeric binder component present inphotopolymerization coatings, and at least one solvent (e) for the saidcomponents (a), (b) and (c). Minor amounts of other components can bepresent in the photopolymerizable compositions, e.g., dyes, thermalpolymerization inhibitors, adhesion promoters, plasticizers, finelydivided particles, etc. The photopolymerizable compositions retain theirbasic properties. For example, the photopolymerizable composition inlayer form has an elongation to break of at least 200%, preferably atleast 300%. In the positive-working coating composition theethylenically unsaturated compound (a) is replaced by at least onephotosolubilizable or photodensitizable material which reacts with theorganic polymeric binder component (c). Optionally a radiation-sensitivecompound or system (b) can be present together with the discrete,substantially nonswellable, crosslinked polymeric beads (d). The coatingcompositions also contain at least one solvent (e) for components (a),(b) and (c).

As noted above, the photopolymerizable composition contains at least oneaddition polymerizable ethylenically unsaturated compound (a) having atleast one polymerizable ethylenic group. Such compounds are capable offorming a high polymer by free-radical initiated, chain propagating,addition polymerization. Preferably, the unsaturated compound (alsoknown as a monomeric compound) has at least two terminal ethylenicallyunsaturated groups, e.g., 2 to 4 groups. The monomeric compounds arenongaseous, i.e., at 20° C. and atmospheric pressure, have a normalboiling point above 100° C. and a plasticizing action on the organicpolymer binder.

Suitable unsaturated monomeric compounds which can be used alone or incombination with other monomers include: t-butyl acrylate andmethacrylate, 1,5-pentanediol diacrylate and dimethacrylate,N,N-diethylaminoethyl acrylate and methacrylate, ethylene glycoldiacrylate and dimethacrylate, 1,4-butanediol diacrylate anddimethacrylate, diethylene glycol diacrylate and dimethacrylate,hexamethylene glycol diacrylate and dimethacrylate, 1,3-propanedioldiacrylate and dimethacrylate, decamethylene glycol diacrylate anddimethacrylate, 1,4-cyclohexanediol diacrylate and dimethacrylate,2,2-dimethylolpropane diacrylate and dimethacrylate, glycerol diacrylateand dimethacrylate, tripropylene glycol diacrylate and dimethacrylate,glycerol triacrylate and trimethacrylate, trimethylolpropane triacrylateand trimethacrylate, pentaerythritol triacrylate and trimethacrylate,polyoxyethylated trimethylolpropane triacrylate and trimethacrylate andsimilar compounds as disclosed in U.S. Pat. No. 3,380,831,2,2-di(p-hydroxyphenyl)-propane, diacrylate, pentaerythritoltetraacrylate and tetramethacrylate, 2,2-di(p-hydroxyphenyl)-propanedimethacrylate, triethylene glycol diacrylate,polyoxyethyl-2,2-di-(p-hydroxyphenyl)-propane dimethacrylate,di-(3-methacryloxy-2-hydroxypropyl)ether of bisphenol-A,di-(2-methacryloxyethyl)ether of bisphenol-A,di-(3-acryloxy-2-hydroxypropyl)ether of bisphenol-A,(di-(2-acryloxyethyl)ether of bisphenol-A,di-(3-methacryloxy-2-hydroxypropyl)ether of tetrachloro-bisphenol-A,di-(2-methacryloxy-ethyl)ether of tetrachloro-bisphenol-A,di-(3-methacryloxy-2-hydroxypropyl)ether of tetrabromo-bisphenol-A,di-(2-methacryloxyethyl)ether of tetrabromo-bisphenol-A,di-(3-methacryloxy-2-hydroxypropyl)ether of 1,4-butanediol, triethyleneglycol dimethacrylate, polyoxypropyltrimethylol propane triacrylate,butylene glycol diacrylate and dimethacrylate, 1,2,4-butanetrioltriacrylate and trimethacrylate, 2,2,4-trimethyl-1,3-pentanedioldiacrylate and dimethacrylate, 1-phenyl ethylene-1,2-dimethacrylate,diallyl fumarate, styrene, 1,4-benzenediol dimethacrylate,1,4-diisopropenyl benzene, and 1,3,5-triisopropenyl benzene. Also usefulare ethylenically unsaturated compounds having a molecular weight of atleast 300, e.g., alkylene or a polyalkylene glycol diacrylate preparedfrom an alkylene glycol of 2 to 15 carbons or a polyalkylene etherglycol of 1 to 10 ether linkages, and those disclosed in U.S. Pat. No.2,927,022, e.g., those having a plurality of addition polymerizableethylenic linkages particularly when present as terminal linkages.Preferred are those wherein at least one and preferably most of suchlinkages are conjugated with a double bonded carbon, including carbondouble bonded to carbon and to such heteroatoms as nitrogen, oxygen andsulfur. Outstanding are such materials wherein the ethylenicallyunsaturated groups, especially the vinylidene groups, are conjugatedwith ester or amide structures. The unsaturated monomeric component ispresent in 5 to 45% by weight based on the total weight of the dryphotopolymerizable layer.

Preferred free radical-generating addition polymerization initiators (b)activatable by actinic light and thermally inactive at and below 185° C.include the substituted or unsubstituted polynuclear quinones which arecompounds having two intracyclic carbon atoms in a conjugatedcarbocyclic ring system, e.g., 9,10-anthraquinone,1-chloroanthraquinone, 2-chloroanthraquinone, 2-methylanthraquinone,2-ethylanthraquinone, 2-tert-butylanthraquinone,octamethylanthraqunione, 1,4-naphthoquinone, 9,10-phenanthrenequinone,benz(a)anthracene-7,12-dione, 2,3-naphthacene-5,12-dione,2-methyl-1,4-naphthoquinone, 2,3-dichloronaphthoquinone,1,4-dimethylanthraquinone, 2,3-dimethylanthraquinone,2-phenylanthraquinone, 2,3-diphenylanthraquinone, sodium salt ofanthraquinone α-sulfonic acid or β-sulfonic acid,3-chloro-2-methylanthraquinone, retenequinone,7,8,9,10-tetrahydronaphthacene-5,12-dione, and1,2,3,4-tetrahydrobenz(a)anthracene-7,12-dione. Other photoinitiatorswhich are also useful, even though some may be thermally active attemperatures as low as 85° C., are described in U.S. Pat. No. 2,760,863and include vicinal ketaldonyl alcohols, such as benzoin, pivaloin,acyloin ethers, e.g., benzoin methyl and ethyl ethers;α-hydrocarbon-substituted aromatic acyloins, including α-methylbenzoin,α-allylbenzoin and α-phenylbenzoin. Photoreducible dyes and reducingagents disclosed in U.S. Pat. Nos.: 2,850,445; 2,875,047; 3,097,096;3,074,974; 3,097,097; and 3,145,104 as well as dyes of the phenazine,oxazine, and quinone classes; Michler's ketone, benzophenone,2,4,5-triphenylimidazolyl dimers with hydrogen donors including leucodyes, and mixtures thereof as described in U.S. Pat. Nos. 3,427,161;3,479,185; and 3,549,367 can be used as initiators. Also useful withphotoinitiators and photoinhibitors are sensitizers disclosed in U.S.Pat. No. 4,162,162. The photoinitiator or photoinitiator system ispresent in 0.05 to 10% by weight based on the total weight of the dryphotopolymerizable layer.

The photopolymerizable composition contains at least one organicpolymeric binder (c), e.g., polyacrylate and α-alkyl polyacrylateesters, e.g., polymethyl methacrylate and polyethyl methacrylate havingan intrinsic viscosity in the range of 0.5 to 3.0; polyvinyl esters,e.g., polyvinyl acetate, polyvinyl acetate/acrylate, polyvinylacetate/methacrylate and hydrolyzed polyvinyl acetate; ethylene/vinylacetate copolymers; polystyrene polymers and copolymers, e.g., withmaleic anhydride and esters; vinylidene chloride copolymers, e.g.,vinylidene chloride/acrylonitrile; vinylidene chloride/methacrylate andvinylidene chloride/vinyl acetate copolymers; polyvinyl chloride andcopolymers, e.g., polyvinyl chloride/acetate; saturated and unsaturatedpolyurethanes; synthetic rubbers, e.g., butadiene/acrylonitrile,acrylonitrile/butadiene/styrene,methacrylate/acrylonitrile/butadiene/styrene copolymers,2-chlorobutadiene-1,3 polymers, chlorinated rubber, andstyrene/butadiene/styrene, styrene/isoprene/styrene block copolymers;high molecular weight polyethylene oxides of polyglycols having numberaverage molecular weights from about 4,000 to 1,000,000; epoxides, e.g.,epoxides containing acrylate or methacrylate groups; copolyesters, e.g.,those prepared from the reaction product of a polymethylene glycol ofthe formula HO(CH₂)_(n) OH, where n is a whole number 2 to 10 inclusive,and (1) hexahydroterephthalic, sebacic and terephthalic acids, (2)terephthalic, isophthalic and sebacic acids, (3) terephthalic andsebacic acids, (4) terephthalic and isophthalic acids, and (5) mixturesof copolyesters prepared from said glycols and (i) terephthalic,isophthalic and sebacic acids and (ii) terephthalic, isophthalic,sebacic and adipic acids; nylons or polyamides, e.g., N-methoxymethylpolyhexamethylene adipamide; cellulose esters, e.g., cellulose acetate,cellulose acetate succinate and cellulose acetate butyrate; celluloseethers, e.g., methyl cellulose, ethyl cellulose and benzyl cellulose;polycarbonates; polyvinyl acetal, e.g., polyvinyl butyral, polyvinylformal; polyformaldehydes.

The binder may also contain sufficient acidic or other groups to renderthe composition processible in aqueous developer. Usefulaqueous-processible binders include those disclosed in U.S. Pat. No.3,458,311 and in U.K. Pat. No. 1,507,704. Useful amphoteric polymersinclude interpolymers derived from N-alkylacrylamides ormethacrylamides, acidic film-forming comonomer and an alkyl orhydroxyalkyl acrylate such as those disclosed in U.S. Pat. No.3,927,199. These patents are incorporated by reference. The numberaverage molecular weight (Mn) of the polymeric binder (and otherpolymers present) is determined by gel permeation chromatographyemploying a polybutadiene standard or other standard known to thoseskilled in the art.

In the photopolymerizable composition are present discrete,substantially nonswellable crosslinked polymeric beads (d). The beadsreplace 15 to 90% by weight of the total amount of binder that isordinarily used in a photopolymerizable composition. Therefore someproperties of the beads as discussed below must be similar to those ofthe binder present in the photopolymerizable composition but unlike thebinder they are insoluble and substantially nonswellable in the solvent,monomer, plasticizer or other component that may be present in thecoating composition. The beads function as part of the binder. They aremutually compatible in the photopolymerizable composition in the broadsense, i.e., "exist together in harmony" with the other components, butare not compatible in the narrow sense, i.e., "form a homogeneousmixture", since this implies mutual solubility. Thus the binder andbeads have a mutual affinity; the binder/monomer combination prior toexposure or the binder/polymerized monomer after exposure wets, adheresor interacts with the surface of the beads. Poor affinity of thephotopolymerizable composition for the beads, i.e., nonwetting of thebeads or nonadhesion to the beads, would result in points of weakness ina dry film prepared from such composition and cannot be tolerated. Thebeads are uniformly dispersed throughout the coating composition andremain dispersed therein as said coating is dried. They also have anegligible effect on the clarity of the coating. The relatively smallparticle size of the beads specified below is important so thatvariations in refractive index between the beads and the remainder ofthe photopolymerizable coating before or after imagewise exposurethereof are not significant.

The most direct way to insure mutual affinity between the binder and thebeads is that they contain groups of generally similar chemical natureor polarity, e.g., oxygen-containing groups or aromatic groups. Forexample, polyester, polyether, polyacid, polyols, etc. binders wouldpreferably use polyacrylate homopolymer or copolymer beads;polycarboxylic acid binders would preferably use beads having a carboxylsurface; polystyrene/polybutadiene/polystyrene block copolymer binderswould preferably use beads rich in divinyl benzene.

With regard to solubility the beads (d) and the binder (c) are quitedifferent. The binder (c) is soluble in the solvent (e) for the coatingand is compatible with or mutually soluble in the monomer (a), initiator(b) and optional ingredients such as plasticizer or dye. The beads,however, do not dissolve in the solvent, are resistant to absorbing orbecoming plasticized by the monomer, other components of thephotopolymerizable composition or mixture of components, and areresistant to being swollen with any of the solvent or components of thephotopolymerizable composition, e.g., at or below room temperature or atelevated temperature present during exposure or used in drying, e.g.,temperatures up to 200° to 500° F. (93° to 260° C.).

The principal reason why the beads should not swell or dissolve in asolvent is that this would adversely affect the drying rate. Inaddition, beads swollen by solvent or the other components of thephotopolymerizable composition become tacky and aggregate thusincreasing their particle size which results in unclear films due tolight scattering, or protrusion from the surface to give a matte ratherthan smooth surface in the dried photopolymerizable layer. Swelling ofthe beads may result in precipitation or coalescence of the beads in thecoating composition. Swelling of the beads by the monomer or othercomponent in the dry photopolymerizable layer will extract monomer,photoinitiator, etc. from the monomer/binder phase, possible over aprotracted period of time, to give changes in physical or sensitometriccharacteristics which would be undesirable in a photopolymerizableelement.

The substantially noswellable crosslinked polymeric beads have anaverage diameter in the range of 0.02 to 4.0 μm, preferably 0.1 to 4.0μm, wherein at least 90% of the beads by population are below 6.0 μm,the beads being insoluble and nonagglomerating in the solvents describedbelow. The crosslinked nonswellable polymeric beads can be homopolymersor copolymers of monomers containing two or more free-radicalpolymerizable double bonds per molecule, e.g., di, tri-, tetra acrylatemonomers, di-, tri-, tetramethacrylate monomers, and copolymers of atleast one of said monomers and at least one monomer having one terminalethylenic group. Preferred crosslinked nonswellable polymeric beads aretaken from the class consisting of homopolymers of tri- andtetraacrylate and tri- and tetramethacrylate monomers, copolymers ofsaid tri- and tetraacrylate and tri- and tetramethacrylate monomers,copolymers of at least one of said tri- and tetraacrylate or said tri-and tetramethacrylate monomers and up to 25% by weight of at least onemonomer having one terminal ethylenic group, copolymers of at least oneof said tri- and tetraacrylate or said tri- and tetramethacrylatemonomers and up to 75% by weight of at least one monomer having twoterminal ethylenic groups or three terminal ethylenic groups differentfrom said triacrylate or trimethacrylate monomers. If the crosslinkedbeads absorb any appreciable amount of the coating solvent, therapid-drying effect will be lost, because it will take the solvent alonger time to be removed from the beads and therefore from thecomposition containing the beads. It is therefore essential to theinvention that the beads should be substantially nonswellable bysolvent. The preparation of the preferred crosslinked nonswellablepolymeric beads and a test for possible swelling of beads are describedin Cohen and Lazaridis U.S. Pat. No. 4,414,278. Also useful arecrosslinked polymeric beads which have their surface hydrolyzed. Thiscan be accomplished by treatment of the polymeric beads containing esterlinkages with sodium hydroxide, potassium hydroxide or other alkalinereagents.

Additional useful crosslinked polymeric beads include: polymers andcopolymers among diacrylates and dimethacrylates of dihydroxy compounds,e.g., diethylene glycol, triethylene glycol, tetramethylene glycol,bisphenol-A, etc., e.g., tetraethylene glycol dimethacrylate,trimethylolpropane triacrylate/styrene (up to 25%) trimethylolpropanetriacrylate (25 to 10)/triethyleneglycol diacrylate (75 to 90),triethylene glycol dimethacrylate/methylmethacrylate (up to 25%),tetraethylene glycol dimethacrylate/methylmethacrylate (up to 25%),divinyl benzene, 1,3,5-trivinyl benzene, triacryloxy cyanurate, triallylcyanurate, triacryloxybenzene, e.g., phloroglucinol triacrylate; andpolymers derived from: acrylates and methacrylates of polyhydroxycompounds such as mannitol, inositol and sucrose, etc.

The total weight percent of the combination of organic polymeric binder(c) and crosslinked beads (d) based on the total weight of components(a) to (d) is 40 to 70% by weight. The crosslinked beads (d) are presentin an amount of 15 to 90% by weight based on the combined weight ofcomponents (c) and (d). As noted in Control Example 1 below themolecular weight of the organic polymeric binder has a bearing on theamount of crosslinked beads that can be present. The preferred weightpercentage of crosslinked beads (d) depends on the molecular weight ofthe binder component (c), e.g., with the major portion of the binderhaving a number average molecular weight up to 40,000, 15 to 40% byweight beads is useful, with the major portion of the binder having anumber average molecular weight over one million (high molecular weightbinders), 30 to 90% by weight beads is useful.

In preparing the photopolymerizable compositions a solvent or mixture ofsolvents (e) for the organic polymeric binder is present. Usefulsolvents include: methylene chloride, 2-ethoxyethanol, methanol,acetone, methyl ethyl ketone, 1,1,1,-trichloroethane, methyl isobutylketone, etc., or a combination of these solvents. The solvent is presentin an amount of 45 to 95% by weight based on the weight of componentsused to prepare the photopolymerizable composition. The solvent isremoved by drying, e.g., with hot air dryers, as is known to thoseskilled in the art.

Not all combinations of solvents and crosslinked beads may be suitablefor securing rapid drying. For example, beads that are made bypolymerization of a significant proportion of acrylates andmethacrylates of polyethylene glycol, e.g., triethyleneglycol diacrylateor tetraethyleneglycol dimethacrylate, will still swell in methylenechloride. Such swellable combinations outside the scope of the inventionmay be found by applying the test for possible swelling of Cohen andLaziridis U.S. Pat. No. 4,414,278 referred to above. If the test showsthat the combination is swellable, either the type of beads may bechanged, e.g., use poly-trimethylolpropane triacrylate beads instead ofpoly-triethyleneglycol diacrylate, or the solvent may be changed, e.g.,use 1,1,1-trichloroethane instead of methylene chloride to obtain anonswellable combination.

In addition to the above major components of the photopolymerizablecomposition optionally minor amounts of the following components canalso be present. Various colorants, e.g., dyes and pigments may be addedto increase the visibility of the image. Photosensitive dye precursorsmay be incorporated to give a visible image upon exposure. Any colorantused, however, should preferably be transparent to the actinic radiationused. Pigments can also be incorporated in the discrete, substantiallynonswellable crosslinked beads which isolates them from chemicalinteraction with the photochemical system.

Preferred thermal polymerization inhibitors which may be presentinclude: p-methoxyphenol, hydroquinone, and alkyl and aryl-substitutedhydroquinones and quinones, tert-butyl catechol, pyrogallol, copperresinate, naphthylamines, β-naphthol, cuprous chloride,2,6-di-tert-butyl-p-cresol, phenothiazine, pyridine, nitrobenzene anddinitrobenzene, p-toluquinone and chloranil and the nitroso compositionsdisclosed in U.S. Pat. No. 4,168,982. Inhibitors, when used, are presentin an amount of 0.001 to 2.0% by weight of the photopolymerizablecomposition.

Adhesion promoters are also useful in the photopolymerizablecomposition. Examples of such adhesion promoters include a small amountof a nitrogen-containing compound of the formula ##STR1## where R isorthoaromatic hydrocarbon nucleus, e.g., benzene or naphthalene; X isCH₂, NH, S, O, or Se; Z is N or C-Y and Y is H, NH₂, alkyl of 1 to 4carbon atoms or halogen, e.g., Cl or Br. A preferred compound isbenzotriazole. The adhesion promoter when used can be present in amountsof at least 0.001% by weight of the monomer and binder component of thephotopolymerizable composition. Suitable compounds are disclosed inHurley et al. U.S. Pat. No. 3,622,334 which is hereby incorporated byreference.

One or more plasticizers compatible with the photopolymerizablecomposition may be present therein to facilitate selective development,improve elasticity or reduce lamination temperature of the dry film.Examples of plasticizers include: dialkyl phthalate, polyethyleneglycol, alkyl phosphates, etc.

If desired, the photopolymerizable compositions can contain immiscibleinorganic fillers or reinforcing agents which have a particle size inthe range of 0.1 to 2.0 μm and are essentially transparent at thewavelengths used for exposure of a layer of the photopolymerizablecomposition and which do not scatter actinic radiation, e.g.,organophilic silicas, silica, powdered glass, etc. Such materials areused in amounts varying with the desired properties of thephotopolymerizable compositions. The fillers are useful in improving thestrength and stiffness of the photopolymerizable layer.

As indicated above positive-working photosensitive coating compositionscontaining crosslinked beads can be prepared using: (a) photosolublepolymers with pendent diazo quinone groups prepared as described in U.S.Pat. No. 3,837,860; (b) photodesensitizable polymers prepared by mixinga bis-diazonium salt with a polymer having pendent hydroxyl or aminogroups as described in U.S. Pat. No. 3,778,270, (c) photosensitivecompositions containing as one component dihydropyridine as described inU.S. Pat. No. 4,271,260, the disclosures of which are incorporated byreference. Photosolubilizable and photodesensitizable resistcompositions are disclosed in U.S. Pat. No. 4,193,797, column 4, line 19to column 5, line 68, the disclosure of which is incorporated byreference.

Photopolymerizable coating compositions containing crosslinked beads canbe prepared as follows: the beads are dispersed with moderate shear inpart of the solvent thereby breaking up any loose aggregations ofparticles that may be present. The dispersion is then combined with theremainder of the solvent and the other ingredients set forth above andin the examples below are added with stirring. The amount of solventused depends to some extent on the method of coating thephotopolymerizable coating composition.

The photopolymerizable coating composition, e.g., prepared as describedabove or by other methods, is filtered, e.g., by passing through anin-line filter with a pore size of 10 μm. The filtered solution may bepumped to a coating apparatus such as a skim coater which may beequipped with an air knife to control coating weight, an extrusion die,a gravure roll, a wire-wound rod, or other coating means known to thoseskilled in the art. The photopolymerizable coating composition can beapplied uniformly to a moving web of film which passes by the coatingunit in an appropriate geometrical relationship. The coated web ispassed into a drier, usually equipped with a heated forced draft airsupply where the air velocity, direction and temperature are controlledto remove the solvent in the coating. The dry web is wound, e.g., onsuitable rolls. At the time of windup, a cover sheet may be laminated tothe dry photopolymerizable surface. Other procedures known to thoseskilled in the art can be used to prepare the dry photopolymerizablefilm.

As indicated previously, in preparing dry film photoresist elements, animage-yielding photopolymerizable stratum on a strippable support ispreferably used. The remaining surface of the supported,photopolymerizable stratum may be protected by a removable cover sheetor when the element is stored in roll form, the stratum surface may beprotected by the contiguous reverse surface of the support. Thephotopolymerizable composition is present in a dry coating thickness ofabout 0.0003 inch (˜0.0008 cm) to about 0.01 inch (˜0.025 cm) or more. Asuitable strippable support which preferably has a high degree ofdimensional stability to temperature changes, may be chosen from a widevariety of films composed of high polymers, e.g., polyamides,polyolefins, polyesters, vinyl polymers, and cellulose esters, and mayhave a thickness of from 0.00025 inch (˜0.0006 cm) to 0.008 inch (˜0.02cm) or more. If exposure is to be made before removing the strippablesupport, it must, of course, transmit a substantial fraction of theactinic radiation incident upon it. If the strippable support is removedprior to exposure, no such restrictions apply. A particularly suitablesupport is a transparent polyethylene terephthalate film having athickness of about 0.001 inch (˜0.0025 cm).

When the element contains no removable, protective cover sheet and is tobe stored in roll form, the reverse side of the strippable supportpreferably has applied thereto a thin release layer of a material, suchas wax or silicone, to prevent blocking with the photopolymerizablestratum. Alternatively, adhesion to the coated photopolymerizable layermay be preferentially increased by flame treating or electricaldischarge treating the support surface to be coated.

Suitable removable, protective cover sheets when used may be chosen fromthe same group of high polymer films described above and may have thesame wide range of thicknesses. A cover sheet of 0.001 inch (˜0.0025 cm)thick polyethylene is especially suitable. Supports and cover sheets asdescribed above provide good protection to the photopolymerizable resistlayer.

Generally, suitable substrates for the process of the inventioninvolving printed circuit formation are those which have mechanicalstrength, chemical resistance and good dielectric properties. Thus, mostboard materials for printed circuits are thermosetting or thermoplasticresins usually combined with a reinforcing agent. Thermosetting resinswith reinforcing fillers are ordinarily used for rigid boards, whereasthermoplastic resin without reinforcements are usually used for flexiblecircuit boards.

Typical board construction involves combinations such as phenolic orepoxy resins on paper or a paper-glass composite, as well as polyester,epoxy, polyimide, polytetrafluorethylene, or polystyrene on glass. Inmost instances, the board is clad with a thin layer of electroconductivemetal of which copper is by far the most common.

Suitable substrates for the process of the invention involvingpreparation of lithographic printing plates are those which havemechanical strength and surfaces which differ in hydrophilicity oroleophilicity from the surfaces of the imaged photosensitive areasthereon formed by laminating a photosensitive layer, exposing anddeveloping said layer. Such substrates are disclosed in U.S. Pat. No.4,072,528. While numerous substrates are satisfactory for this purposethin anodized aluminum plates such as those disclosed in U.S. Pat. No.3,458,311 are particularly useful. Anodized and silicated aluminumplates are also useful.

It will be recognized by those skilled in the art that it will bepreferable for the printed circuit substrate surface which is to belaminated to be clean and free of any extraneous material. For thisreason, it will frequently be desired to clean printed circuitsubstrates prior to lamination by one or more of the several cleaningprocesses which are well-known in the field of printed circuit boardmanufacture. The particular type of cleaning depends upon the type ofcontamination, e.g., organic, particulate or metallic. Such methodsinclude degreasing with solvents and solvent emulsions, mechanicalscrubbing, alkaline soaks, acidification and the like, followed byrinsing and drying.

After preparation of the element and lamination of thephotopolymerizable layer to a printed circuit board if the element is tobe used as a dry photoresist, the photopolymerizable layer is imagewiseexposed to actinic radiation through a suitable image, e.g., imagebearing transparency, positive or negative or a suitable photomask. Thesource of actinic radiation generally furnishes an effective amount ofradiation in the ultraviolet range. Suitable sources include: carbonarcs, mercury-vapor arcs, fluorescent lamps with specialultraviolet-emitting phosphors, argon glow lamps, electronic flash unitsand photographic flood lamps, etc. The amount of exposure required forsatisfactory reproduction of a given photopolymer layer is a function ofexposure time, type of radiation source used, and distance between theradiation source and layer surface. In general, exposure times rangefrom 0.5 to 10 minutes or more using standard commercial radiationsources.

After imagewise exposure the unexposed areas of the photopolymerizedlayer are removed by liquid development, e.g., a solvent or solventmixture for the organic polymeric binder component. The development mayoccur in any convenient manner, e.g., by pouring, immersion, spraying,or roller application. Brushing may aid in removal of the unpolymerizedor uncrosslinked portions of the composition. Development can occur withwarm solutions and the time varies depending on the photopolymerizablelayer, e.g., its composition, thickness, etc. Useful development rangescan be in the range of from 5 seconds to 25 minutes. After developmentthe element can be dried, if necessary, e.g., in air including placingin front of a fan.

A preferred embodiment of the photopolymerizable composition isillustrated in Example 1, wherein the crosslinked polymeric beads arehomopolymers of trimethylolpropane triacrylate.

INDUSTRIAL APPLICABILITY

The photopolymerizable compositions of this invention having a portionof the organic polymeric binder replaced by the discrete, substantiallynonswellable crosslinked beads have been found to dry appreciably fasterthan a similar photopolymerizable composition containing none of thecrosslinked beads. The photopolymerizable compositions of the inventioncan be manufactured into dry film photoresists or dry photopolymerizableelements more quickly and efficiently than the compositions of the priorart. The dry photoresists are used in the preparation of printedcircuits. Such photoresists are capable of being processed more rapidly.In element form a layer of the dry photopolymerizable composition ispresent between a support, e.g., film or sheet, and a removable coversheet. Such an element when used to prepare a printing plate may havethe support permanently adhered to the photopolymerizable layer. Whenthe element is used as a dry film photoresist the support is capable ofbeing removed from the photopolymerizable layer without damage thereto.The photopolymerizable layer retains desirable properties even thoughthe crosslinked polymeric bead are present in relatively large amounts.Thus the photographic speed, adhesion to copper, clarity or resolutionand flexibility of the photopolymerizable layer of the invention areretained.

While the photopolymerizable coating compositions containing thediscrete, substantially nonswellable crosslinked beads arenegative-working systems, similar advantages would apply forphotosensitive compositions containing positive-working photosensitivesystems provided that the same critical criteria for the solvent solublebinder and crosslinked beads described above are met.

The use of the crosslinked beads in positive-working photosensitivecoating compositions and as dry film elements is particularlyadvantageous where the photosensitive films are being designed for useas photoresist films in making printed circuit boards. Such films aregenerally thicker than positive-working coatings used formicroelectronic applications. It is therefore advantageous to be able tocoat and dry these relatively thick coatings rapidly to achieve superiorphysical properties in the resulting dry film elements. Useful types ofpositive-working dry film formulations particularly useful as dry filmresists are described in Cohen et al. U.S. Pat. No. 4,193,797 and Abeleet al. U.S. Pat. No. 4,271,260. These patents are incorporated byreference.

Positive-working coating compositions which are based onphotosolubilization of diazo quinone compounds are also useful with thediscrete, substantially nonswellable crosslinked beads described herein.The diazo quinone compounds would be used in place of the ethylenicallyunsaturated compound normally present in negative-workingphotopolymerizable compositions. The separate photoinitiating systemnecessary in the negative-working compositions is often not required.

EXAMPLES

The invention is illustrated by but is not intended to be limited to thefollowing examples wherein the parts and percentages are by weight. Thepolymeric molecular weights are number average molecular weights.Inherent viscosity is measured on a solution containing 0.25 g ofpolymer in 50 ml of methylene chloride, at 20° C. using a Cannon-Fenskeviscometer. The intrinsic viscosity set forth in the examples isdetermined by extrapolation of specific viscosity to zero concentration.Specific viscosity is (n-n_(o))/n_(o) where n is the viscosity of thesolution and n_(o) is the viscosity of pure solvent both determined at25° C. using an Ostwald viscosimetric pipette. The elongation to breakof dry photopolymerizable layers is determined according to ASTMD412-75. Samples of the coating compositions are coated on film supportsusing a 0.008 inch (0.20 mm) doctor knife and dried at room temperaturefor 48 hours. The coating samples are stripped from their supports andare laminated together to provide a layer thickness of about 0.006 inch(about 0.15 mm) unless otherwise stated. A 1 inch by 3 inch (2.54 cm by7.62 cm) piece of the laminate is placed in the jaws of an InstronTester Model TM at initial separation of one inch (2.54 cm) with acrosshead speed of one inch/minute (2.54 cm/minute).

EXAMPLE 1 A. Preparation of Beads

To a one-liter beaker containing 500 g of trimethylolpropanetriacrylate, 193 ppm of hydroquinone and 130 ppm of p-methoxyphenol wasadded 5.7 g of benzoyl peroxide. The mixture was stirred at roomtemperature until the benzoyl peroxide was dissolved, and the solutionwas used within an hour after solution was complete. A solution of 2.5 gof sodium di-octyl sulfosuccinate and 4.2 g of a surfactant (HostaponTHC, manufactured by American Hoechst, Somerville, N.J.) containing 2.5g of the sodium salt of oleyl methyl tauride in 1200 ml of water wasprepared in a stainless steel beaker. The solution was stirred at lowspeed with a 1/2 horsepower Eppenbach mixer while the peroxide/monomersolution was added. The speed of the mixer was then slowly increased(over a period of about 10 minutes) by raising the input voltage of themixer to about 70 volts. The speed was held at this point for about onehour. The stainless steel can containing the creamy white emulsion wasthen covered and held in a water bath at 60° C. for 72 hours. Thepolymerized emulsion was allowed to cool and centrifuged. The supernatewas discarded and the polymer cake was stirred with about one liter ofwater and centrifuged again. The stirring with water and centrifugingwas repeated twice more, and the cake of polymer beads was allowed toair dry. The dried polymer was easily redispersed either in water or inorganic solvents such as methylene chloride, acetone or ethanol by usinga household type blender-homogenizer at low speed. The mean particlesize based on population determined using a Coulter Counter manufacturedby Coulter Electronics, Inc., Hialeah, Fla. was 0.66 μm and the meanvolume particle size was 1.2 μm.

B. Preparation of Coating Dispersions for Photoresist

A stock dispersion of beads in methylene chloride was made by stirringtogether 26.8 parts of the dried beads, prepared as described above, and66.6 parts of methylene chloride. The dispersion was filtered through anylon felt filter pad with substantially no retention of solid materialand 5.5 parts of polymethylmethacrylate having an inherent viscosity of1.25 and 1.2 parts of polymethylmethacrylate having an inherentviscosity 0.5 were dissolved in the suspension. The polymers were addedto increase the stability of the dispersion, but this was found not tobe necessary.

Coating compositions were prepared containing the ingredients listed inTable 1. Coating dispersion A containing no crosslinked beads was usedas a control. In coating dispersions B and C, 40% and 20% respectively,of the total weight of binder and beads was crosslinked beads. Thiscorresponds to about 24.24 and about 12.12%, respectively, based on thetotal weight of components (a), (b), (c) and (d).

                  TABLE 1                                                         ______________________________________                                        COATING FORMULATIONS                                                          Ingredient     A          B        C                                          ______________________________________                                        Methylene chloride                                                                           10728      10728    10728                                      2-Ethoxyethanol                                                                              1192       1192     1192                                       Polymethyl-    3270       1962     2616                                       methacrylate.sup.1                                                            Polymethyl-    700        420      560                                        methacrylate.sup.2                                                            Crosslinked beads as                                                                         --         1588     794                                        described above                                                               Trimethylolpropane                                                                           1050       1050     1050                                       triacrylate                                                                   Tetraethylene glycol                                                                         1050       1050     1050                                       diacrylate                                                                    Michler's ketone                                                                                8.4        8.4      8.4                                     Benzophenone   280        280      280                                        Bis(2-o-chlorophenyl-                                                                        175        175      175                                        4,5-bis-phenyl)                                                               imidazole                                                                     Tris-(4-diethylamino-                                                                          10.5       10.5     10.5                                     o-tolyl) methane                                                              4,4'4"-Methylidyne                                                                              7.0        7.0      7.0                                     tris (N,N--dimethyl                                                           aniline)                                                                      Victoria Green, C.I.                                                                            2.45       2.45     2.45                                    Pigment Green 18                                                              Monastral Green Pigment,                                                                        7.80       7.80     7.80                                    C.I. Pigment Green 7                                                          Mixture of ortho                                                                               420.0      420.0    420.0                                    and para-toluene                                                              sulfonamide                                                                   Benzotriazole    14.0       14.0     14.0                                     p-Toluene sulfonic                                                                               3.5       3.5      3.5                                     acid                                                                          Total          18919.0    18919.0  18919.0                                    ______________________________________                                         .sup.1 Inherent viscosity 1.25                                                .sup.2 Inherent viscosity 0.50                                           

The solutions were each extrusion coated to give a dry coating thicknessof 50.8 μm. Samples were coated at 4.57 m/min; pump speeds were adjustedin each case until the dry coating thickness was 50.8 μm. Pump speedswere then calculated to secure the same coating thickness at 6.10, 7.62,9.14 and 10.67 m/min. Subsequent thickness measurements confirmed theconstant coating thickness. After coating, the coated web was led into athree-chambered dryer. Temperatures in the three successive chamberswere held at 38°, 66° and 121° C. Air velocities and temperatures in thethree zones were held constant throughout the drying. Upon exiting fromthe dryer, the coated web was laminated with polyethylene film, 25 μmthick, and wound up. All of the coatings from a given coating dispersionwere successively wound on the same core. Immediately after the lastcoating (at the farthest coating speed), samples were taken. A 7-10meter sample of each coating was wound on a core which had beenpreviously covered with aluminum foil, and after winding the sample,aluminum foil was wrapped around the outside to prevent escape of anysolvent vapor. Samples were analyzed for residual solvent by a procedurebased on heating a sample of the coated material in a closed volume, andanalyzing the vapor obtained by infrared absorption for the two solventspresent, methylene chloride and 2-ethoxyethanol. The percentage of theresidual amount of each solvent was then calculated and is shown inTable 2.

                  TABLE 2                                                         ______________________________________                                        Residual Solvent from Coatings                                                Made at Various Coating Speeds                                                         Coating         Coating     Coating                                  Coating  Dispersion      Dispersion  Dispersion                               Speed    A               B           C                                        (m/min)  M      E        M    E      M    E                                   ______________________________________                                        4.57     0.19   0.19     0.02 0.02   0.12 0.13                                6.10     0.47   0.24     0.03 0.03   0.14 0.15                                7.62     0.42   0.22     0.05 0.04   0.12 0.16                                9.14     0.35   0.28     0.09 0.16   0.28 0.20                                10.67    0.88   0.38     0.17 0.16   0.42 0.27                                ______________________________________                                         M is percent methylene chloride content                                       E is percent 2ethoxyethanol content                                      

From Table 2, it can be seen that there is a marked difference betweenthe amounts of residual solvent obtained from Coating Dispersion B atany stated coating speed and those of Coating Dispersion A. The amountof residual solvent obtained from Coating Dispersion A at 4.57 m/min isgreater than that obtained when Coating Dispersion B is coated at 10.67m/min, i.e., more than twice as fast. Coating Dispersion B, in which 40%of the total weight of polymeric binder and beads was crosslinkedpolymer beads, required less than half as much time to dry as CoatingDispersion A (control) to the extent that the total residual solvent wasreduced to less than about 0.4%. Coating Dispersion C, in which 20% ofthe total weight of polymeric binder and beads was crosslinked polymerbeads, gave results intermediate between those from Coating DispersionsA and B. Coatings from Coating Dispersion A contained bubble defectsranging from 0.3dm² when coated at 4.57 m/min to 20/dm² when coated at10.67 m/min. No bubble defects were found in coatings from CoatingDispersions B and C.

Samples of Coating Dispersions A, B and C, each made at 4.57 m/min weretested as dry film photoresists. Lamination of the dry films to copperwas conducted at 220° F. (104.4° C.). The film flexibility, photospeed,image quality, etching results with FeCl₃ and plating with copper weresubstantially the same for each of the three photoresists. Thedevelopment times required for photoresists prepared from CoatingDispersions A and B were as follows:

    ______________________________________                                                       Time (seconds)                                                 ______________________________________                                        Coating Dispersion A                                                                           105                                                          Coating Dispersion B                                                                            68                                                          ______________________________________                                    

The development occurred in a spray processor wherein the dry filmlaminate is held and methyl chloroform solvent is pumped to spraynozzles therein to deliver the solvent in a broad pattern with amoderately high velocity. The elongation to break of dry coating A, Band C was as follows:

    ______________________________________                                                Elongation to Break (%)                                               ______________________________________                                        A         360                                                                 B         670                                                                 C         437                                                                 ______________________________________                                    

EXAMPLE 2 A. Procedure

Crosslinked polymeric beads were treated to hydrolyze surface estergroups to carboxyl groups. 40.0 Gram portions of beads prepared asdescribed in Example 1 were stirred with 48.4 g of 4% aqueous sodiumhydroxide for 5 hours at room temperature (H); with 33.3 g of 10%aqueous sodium hydroxide for 20 minutes at 45°-57° C. (I); with 48.4 gof 4% aqueous sodium hydroxide for 40 minutes at 57°-62° C. (J), with48.4 g of 4% aqueous sodium hydroxide for 50 minutes at 60°-65° C. (K)and with 48.4 g of 4% aqueous sodium hydroxide for about four hours at60°-70° C. (L). After the treatment each slurry was poured into about100 ml of ice-cold water and centrifuged. The viscosity of thesupernatant liquid was measured with and Ostwald pipette. Theviscosities do not differ significantly from the viscosity of similarlydiluted sodium hydroxide (less than 1.2 cps), except for sample L, whichhad a viscosity of 13.4 cps. This indicated that hydrolysis wasrestricted to the surface in samples H to K, but that in sample L, thehydrolysis had gone too far, resulting in polymer (polyacrylic acid) insolution. The centrifuged beads were wased four times by stirring with120 ml of water and recentrifuging. The washed samples were then allowedto dry. The presence of carboxyl groups in the samples was demonstratedby stirring 0.1 g of the dry powder with one or two milliliters of waterand then adding 10.0 ml of a solution of 0.1 g of methylene blue and 20ml of pH7 buffer in 80 ml of water. The mixture was centrifuged, thesupernate was discarded, and the precipitate was washed three times bystirring with 35 ml of water and recentrifuging. The precipitate wasthen dried on filter paper. The depth of blue color increased in theorder H to K; sample H was pale blue and sample K was quite dark.

B. Preparation and Use of Beads of the Invention

Samples were prepared like sample K above except in 500 g batches. Asolution of 41.6 g of sodium hydroxide in 375 ml of water was heated to70° C. and 500 g of polymeric beads as described in Example 1 were addedwith stirring. The temperature was raised from the resultant 53° to 60°C. over 7 minutes and the slurry formed was stirred at 60°-65° C. for 50minutes. The slurry was added to 1500 ml of ice water and thencentrifuged. Viscosity of the supernate was not significantly differentfrom that of similarly diluted aqueous sodium hydroxide. The precipitatewas stirred with about one liter of water and the pH adjusted to 2.5 togive carboxylic acid groups on the surface. The slurry was furtherdiluted to about four liters and centrifuged. The beads were washed fourtimes by diluting to about four liters and recentrifuging, and finallywere air dried. Yield was about 480 g.

A comparison was made of the drying rate of a control composition as inCoating Dispersion A of Example 1, and a composition like CoatingDispersion B of Example 1 except that instead of the polymeric beads ofthat example, 40% of the total weight of polymer binder and beads wasbeads with a carboxyl (hydrolyzed) surface made as described above. Theresults were similar to those of Example 1, the composition containingthe crosslinked beads gives about the same amount of residual solventwhen coated at 9.14 m/min as the control does at 4.57 m/min, i.e., itdries about twice as fast. This composition was also compared with acontrol coating used as a dry film photoresist. Similar results wereobtined for photospeed and quality of etching and of plating, and instripping of the photopolymer layer from the completed circuit asdescribed in Example 1. The elongation to break of the lab coating was570%.

EXAMPLE 3

A coating composition was prepared as follows:

    ______________________________________                                                             Parts                                                    ______________________________________                                        Crosslinked beads as described in Ex. 1                                                              55.52                                                  Trimethylolpropane triacrylate                                                                       13.10                                                  Tetraethylene glycol diacrylate                                                                      13.10                                                  High molecular weight  6.620                                                  polymethylmethacrylate.sup.3                                                  Michler's ketone       0.106                                                  Benzophenone           3.517                                                  Bis(2-o-chlorophenyl-4,5-bis-phenyl)                                                                 2.193                                                  imidazole                                                                     Tris-(4-diethylamino-o-tolyl)methane                                                                 0.132                                                  4,4'4"-Methylidyne tris (N,N--dimethyl                                                               0.088                                                  aniline)                                                                      Victoria Green, C.I. Pigment Green 18                                                                0.031                                                  Monostral Green Pigment, C.I. Pigment                                                                0.098                                                  Green 7                                                                       Mixture of ortho and para-toluene                                                                    5.275                                                  sulfonamide                                                                   Benzotriazole          0.176                                                  p-Toluene sulfonic     0.044                                                  acid                                                                          Total                  100.000                                                Solvent, CH.sub.2 Cl.sub.2                                                                           196.2                                                  ______________________________________                                         .sup.3 Intrinsic viscosity, 2.7                                          

The beads are added as a 28.9% slurry in methylene chloride and thepolymethylacrylate as 9% solution. These compositions are combined(already contained required amount of solvent) and the remainingingredients are added. The coating composition contains 33.8% activeingredients.

A control coating composition was prepared like Coating Dispersion A ofExample 1, except that instead of the mixture of methylene chloride and2-ethoxyethanol, and solvent was 20732 g of pure methylene chloride togive a solution with 33.8% active ingredients. Drying rates are comparedas in Example 1, using the same coater and three-stage dryer, andcoating 50.8 micrometers thick as in Example 1. The amount of residualsolvent from the bead-containing composition is significantly lower whencoated at 10.67 m/min than the control coated at 4.57 m/min and is 0.10%as compared to 0.20% of the control. The dry coating was laminated tocopper board and processed as described in Example 1 to give a coppercircuit on the board. The elongation to break of a dry coatingcomposition is 700%.

EXAMPLE 4

The preparation of crosslinked beads as described in Example 1 isrepeated, except that instead of 500 g of trimethylpropane triacrylate,500 g of triethylene glycol diacrylate is used in one experiment (F) anda mixture of 250 g of trimethylolpropane triacrylate and 250 g oftriethylene glycol diacrylate is used in another experiment (G). Coatingcompositions are prepared like those of Coating Dispersion B, Example 1,except that in one, the crosslinked beads used are those of CoatingDispersion G and in a second one, those of Coating Dispersion F. Acoating composition like Coating Dispersion A in Example 1 is coated asa control. The results are similar to those described above for thecoating dispersion containing the crosslinked beads (G); at 11 m/min theresidual solvent is about 0.4%, while Coating Dispersion A againrequires about 5 m/min to achieve that level. In the case of thecrosslinked beads (F), however, the rate of drying must be reducedalmost to the rate for Coating Dispersion A to secure the 0.4% level ofresidual solvent. Upon applying the swelling test described in U.S. Pat.No. 4,414,278, it is found that the crosslinked beads G do not swell inmethylene chloride whereas the crosslinked beads (F) swell about 40% inthis test. This example using crosslinked beads (F) is repeated exceptthat the methylene chloride solvent is replaced by an equal volume of1,1,1-trichloroethane, in which beads (F) do not swell according to theswelling test. A coating composition is made similar to CoatingDispersion A, but using 1,1,1,-trichloroethane instead of methylenechloride. The drier temperature is raised to accommodate thehigher-boiling solvent. The 1,1,1,-trichloroethane coating dispersionmade like Coating Dispersion A dries at approximately 5 m/min. and theCoating Dispersion with beads (F) at approximately 10 m/min for aresidual solvent control of 0.4%. That is, the drying is twice as fastto attain a 0.4% solvent level. These compositions are laminated tocopper as described above, and a suitable photoresist image obtained onthe copper after exposure and development. The elongation to break ofthe dry coating compositions corresponding to F and G is greater than400%.

EXAMPLE 5

An electrical printed circuit is made as follows: twelve parts of2-diazo-1-naphthol-4-sulfonyl chloride prepared as described in U.S.Pat. No. 3,837,860 is added to 20 parts of dioxane, and the mixture isslowly added to a 50 parts dioxane solution containing 2.0 parts of acopolymer of methyl methacrylate and hydroxymethyl methacrylate (90/10).The addition of 10 parts of a 1% solution of sodium carbonate turns thesolution purple. A copolymer is thereby formed having pendent diazoquinone groups. The copolymer is precipitated with water, is collectedand is dissolved in dioxane containing dispersed therein 9.3 parts ofcrosslinked polymeric beads as described in Example 1. This coatingcomposition contains about 20.0% solids in dioxane and is coated asdescribed in Example 1 onto a moving polyethylene terephthalate web at4.57 m/min and is dried. The drying is appreciably faster than that of asimilar coating composition containing 20% diazo quinone polymer withoutbeads present. A sample of the dry coating composition containing thecrosslinked polymer beads with its support film is laminated to a cleanpiece of copper-clad, epoxy-Fiberglass board with the surface of thephotosensitive layer in contact with the copper surface. The laminationis carried out with the aid of rubber covered rollers at 120° C. Theresulting resist covered element is image-exposed through a transparencywith a positive image of the electrical circuit pattern on it for threeminutes using a 500-watt mercury light source at a distance of 16 inches(40.64 cm). After exposure, the polyethylene terephthalate support filmis stripped from the resist. The board is then developed by washing outthe exposed areas with a 5% aqueous trisodium phosphate. This stepleaves the resist on the copper in the pattern of the opaque areas ofthe exposing transparency, thus giving a positive image. The copperareas exposed by washout of the soluble resist corresponding to theclear areas of the exposing transparency are etched away down to theepoxy-Fiberglass by placing the board in a 45° Baum/e/ ferric chloridesolution. This leaves the resist-covered copper conducting pattern onthe Fiberglass board. The resist is finally removed from the coppercircuit using a commercially available stripping agent of methanol anddichloromethane 10/90.

CONTROL EXAMPLE 1

This is a control example. Two coating compositions are prepared asfollows:

    ______________________________________                                                         Parts                                                                         D (Control)                                                                             E                                                  ______________________________________                                        Copolymer of styrene/maleic anhy-                                                                30.00       4.05                                           dride (1.4/1.0) esterified with                                               a butanol mixture, molecular                                                  weight 10,000, Acid No. 190                                                   Copolymer of methyl                                                                              20.0        2.69                                           methacrylate (71%)/-                                                          ethyl acrylate (17%)/-                                                        acrylic acid (12%),                                                           molecular weight 200,000,                                                     acid No. 100, glass                                                           transition temp 70° C.                                                 Copolymer of methyl                                                                              14.72       1.98                                           methacrylate(55)/                                                             ethyl acrylate(35)/acrylic                                                    acid(10), molecular weight                                                    30,000, acid No. 80, glass                                                    transition temp. 50° C.                                                Crosslinked beads as           56.00                                          described in Ex. 1                                                            Trimethylol propane triacrylate                                                                  27.00       27.00                                          Michler's ketone   0.50        0.50                                           Benzophenone       5.00        5.00                                           Bis(2-o-chlorophenyl-4,5-bis-                                                                    2.00        2.00                                           phenyl)imidazole                                                              Tris-(4-diethylamino-                                                                            0.20        0.20                                           o-tolyl)methane                                                               Benzotriazole      0.40        0.40                                           Victoria Green, C.I. Pigment                                                                     0.05        0.05                                           Green 18                                                                      1,4,4-Trimethyl-2,3-diazabicyclo                                                                 0.03        0.03                                           (3.2.2)-non-2-ene 2,3-dioxide                                                 p-Toluene sulfonic acid                                                                          0.10        0.10                                           Total              100.00      100.00                                         Methylene chloride 186.60      186.60                                         Methanol           16.23       16.23                                          ______________________________________                                    

Coatings are made as described in Example 1 and also at 4.0 m/min and at12.2 m/min. The total residual solvent for Coating Dispersion E at 12.2m/min is still lower than that for Coating Dispersion D at 4.0 m/min(0.3%). That is, the time required to dry Coating Dispersion E to aresidual solvent level of 0.3% is less than one-third of the timerequired to dry Coating Dispersion D to that same level. Both coatingsare laminated to copper, exposed 30 seconds through a transparency witha 2000 watt Berkey-Ascor mercury-xenon arc, developed for 30 seconds inthe spray-processor described in Example 1 with 1% aqueous sodiumcarbonate at 43° C., rinsed and dried to give a photoresist image on thesurface of the copper. The elongation to break of the dry coatingcompositions was: 245% for D and 10% for E (layer thickness of E was0.12 inch (0.30 mm). This low elongation value for E indicates a brittlecoating. This control shows that relatively low molecular weightpolymeric binders cannot be replaced by about 85% crosslinked beads.

CONTROL EXAMPLE 2

Three coating dispersions are prepared. Two coating dispersion wereCoating Dispersions A and B prepared as described in Example 1. Thethird coating dispersion was Coating Dispersion M prepared in a manneridentical to the preparation of Coating Dispersion B but usingpolyethylene beads of about 2.0 μm mean particle size. The coating M wasobserved to be very brittle. A 0.006 inch (0.15 mm) or 0.02 inch (0.30mm) laminate was very difficult to manipulate without breaking, similarto coating E of Control Example 1.

We claim:
 1. A positive-working photosensitive element comprising asupport bearing a releasably bonded dry layer of a positive-workingcomposition having an elongation at break above about 200% consistingessentially of (a) at least one photosolubilizable orphotodesensitizable material and (b) at least one organic polymericbinder, components (a) and (b) being present in amounts of 50 to 95% and5 to 50% by weight, respectively, based on the total weight ofcomponents (a) and (b); a radiation sensitive compound or systemactivatable by actinic radiation, 0 to 10% by weight based on the totalweight of the composition; and (c) discrete, substantially nonswellablecrosslinked polymeric beads having an average diameter in the range of0.02 to 5.0 μm, wherein at least 90% of the beads by population arebelow 0.6 μm, the beads being insoluble and nonagglomerating in asolvent for the organic polymeric binder component, said crosslinkedpolymeric beads are taken from the class consisting of homopolymers andcopolymers of tri-, and tetraacrylate, and tri-, and tetramethacrylatemonomers which contain three or more free-radical polymerizable doublebonds per molecular, copolymers of at least one of said acrylate andmethacrylate monomers and up to 25% by weight of at least one monomerhaving one terminal ethylenic group, and copolymers of at least one ofsaid acrylate and methacrylate monomers and up to 75% by weight of atleast one monomer having two terminal ethylenic groups, the weight ofcomponent (c) being 20 to 65% by weight based on the total weight of thecomposition.
 2. A positive-working photosensitive element according toclaim 1 wherein component (a) is a quinone diazide compound andcomponent (b) is a hydroxyl-containing polymeric binder.
 3. Apositive-working photosensitive element according to claim 1 wherein thepositive-working composition contains (d) a radiation sensitive compoundor system activatable by actinic radiation in an amount of 0 to 10% byweight based on the total weight of composition.
 4. A positive-workingphotosensitive element according to claim 1 wherein the crosslinkedpolymeric beads are trimethylolpropane triacrylate beads.
 5. Apositive-working photosensitive element according to claim 1 wherein thecrosslinked polymeric beads have their surface hydrolyzed.
 6. Apositive-working photosensitive element according to claim 5 wherein thehydrolyzed surface contains acidic groups.
 7. A positive-workingphotosensitive element according to claim 5 wherein the surface of thebeads is treated with sodium hydroxide or potassium hydroxide.
 8. Aprocess for forming a positive resist image on a substrate whichcomprises(a) applying to said substrate the surface of thephotosensitive surface positive-working element of claim 1; (b) forminga firm bond between the positive-working element and the substrate; thenin either order of (c) and (d); (c) exposing the positive-workingelement, imagewise, to actinic radiation to form an image; (d) removingthe support from the surface of the positive-working layer by mechanicalstripping or liquid dissolution; and then, (e) washing away the areas ofthe positive-working layer which still remain soluble after exposure toform a positive resist image on the substrate.
 9. A process according toclaim 8 wherein the surface of the substrate unprotected by the resistimage is chemically modified by etching or plating.